Chelsea and Arsenal both have lot of African fans or fans with African roots. This may be due to the considerable number of Africans that have played for them over the last few years eg. Drogba, Essien, Toure, Eboue, Lauren, Mikel, Adebayor, Vieira (Senegalese originally). I was speaking to a Chelsea fan I work with recently about this (black fella by the way, but actually of Afro-Carribean descent), and he was saying how the big European-based African players (like Drogba, Essien and Eto'o in particular) are like Gods in Africa. So I suppose it's no surprise that English football fans of African ethnicity gravitate towards the likes of Chelsea and Arsenal.